It is well known that ultraviolet (UV) irradiation may be used to reduce or eliminate the various minerals, microorganisms, and other contaminants in water. However, all of the current humidifiers that utilize a UV lamp only sterilize the humidifying water as the water exits from the water reservoir and flows toward the heating or vaporizing unit. The flaw in these humidifiers is that the water inside the reservoir is never irradiated. Over time, therefore, mineral deposits inside the reservoir would either clog up the aperture that allows outflow of the water, cause corrosion to various parts in the humidifier or, at the very least, render the walls and bottom of the reservoir covered with unsightly mineral buildup.